Feeding during training leads to the same problems seen in the section on the pre-training meal, although Rehrer (2001) reports a decrease in the extent of blood diversion during extensive metabolic loading (and, consequently, a reduction in the extent of associated intestinal disorders) in athletes who have consumed carbohydrates together with electrolytes during training. Regardless of this, however, for some athletes, i.e. precisely those practising disciplines involving a considerable metabolic load (emphasis on endurance), it is recommended to at least consider consuming drinks with macronutrients during training. The aim is to have a new energy supply ready when the one previously built up is about to run out. In this regard, in addition to the already mentioned carbohydrates, the most important macronutrients to take with the drink in this context are the proteins.

On carbohydrate intake during training

  With regard to the former, studies show that an intake of carbohydrates during an endurance load can double the rate of sugar utilisation (from 1g/min. to 2g/min.). Furthermore, keeping blood glucose constant provides the muscles with readily utilised blood glucose, preventing depletion of the glycogen reserves contained therein.

Optimal frequency of intake

  Now, considering that carbohydrates ingested during the application of a metabolic load begin to be used by the body about half an hour after intake, and that their effectiveness is at its maximum two hours later, the recommendation not to wait until you run out of energy to feed is particularly important. Instead, it is a good idea to consume carbohydrate foods as consistently as possible during training.

Optimal intake quantity

  With regard to the optimal amount of carbohydrates to take, it is generally believed that the muscles of an athlete with a fair amount of experience in endurance training consume around 1g of glucose per minute. It is clear, therefore, that taking in more than 60g of sugar in one hour is unnecessary. Having put this general limit in place, each athlete should work out what their carbohydrate requirement is specifically for the training period and, where general dietary guidelines allow, try to meet at least half of it, having, as always, the osmolarity of the drink under control.

Preferred carbohydrate sources

  Finally, as for the selection of carbohydrate sources, it is good to prefer carbohydrates that can be made bioavailable in as short a time as possible. The glycaemic index, of course, must therefore be high. In addition, it is desirable that a mixture of various sugars (e.g. glucose, sucrose) be taken in, so that each of them can reach the bloodstream following different digestive pathways, and therefore travelled simultaneously.

On protein intake during training

  Protein intake during training load essentially has two benefits: firstly, when proteins are taken during training, they can hinder the increased production of serotonin (a neurotransmitter vector of fatigue) in the brain, delaying the onset of fatigue; moreover, when taken together with carbohydrates, they reinforce the protective action that the latter have on muscle structure. However, the recommendation is important not to replace, especially in the context of metabolic loading (endurance work), carbohydrates with protein, except, at the very least, in a small part. Instead, the best thing to do would be to add them to carbohydrates, always checking the osmolarity of the drink during metabolic load.